Method and system for testing the quality of a signal transmission in a communication system

ABSTRACT

A signal comprising a succession of first bit sequences Xn is generated. Each Xn with n≥1 is determined from the preceding Xn−1 using a deterministic algorithm P. The signal is transmitted from a transmitter through the communication system and received as a second bit sequence Xn′ by a receiver. For each received Xn′, the method comprises determining a first group of candidates corresponding to a plurality of possible first bit sequences Xn,i that could have been sent from the transmitter device and changed into the second bit sequence Xn′ according to an acceptable modification in the communication system; determining a second group of candidates from candidates determined for the preceding index n−1 and using P; determining a third group of candidates by intersecting the first group of candidates and the second group of candidates; checking the third group.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to EP Application No. 18214279.4, filedon 19 Dec. 2018.

FIELD OF THE DISCLOSURE

The present disclosure relates to the field of testing the quality of asignal transmission through a communication system, network,architecture or the like, for example in an automotive audioarchitecture.

BACKGROUND OF THE DISCLOSURE

There are different known techniques for testing the quality of adigital signal transmission through a network, a communication system,architecture or the like.

A well-known technique consists in measuring a bit error rate (BER)during transmission and uses PRBS (Pseudo Random Binary Sequence), thatare binary sequences that, while generated with a deterministicalgorithm, are difficult to predict and have statistical behaviorsimilar to truly random sequences, in order to evaluate transmissionalterations through a network.

More precisely, on a transmitter device side, the pseudorandom binarysequences are generated using a source register such as a linearfeedback shift register (LFSR). In practice, a sequence generatingfeedback polynomial, constituting a deterministic algorithm, operates onbits placed in a set of specific bit positions of the source register,called the “taps”, in order to generate a new bit. Then, the sourceregister shifts to the right, outputs the rightmost bit and the newlygenerated bit is fed back into the leftmost bit position which rank is“0”.

The feedback polynomial is chosen according to the length of the sourceregister so as to create a very long cycle (seemingly random) of bitsbefore the source register returns to its initial state. For instance,for a 16 bit register, the maximal length feedback polynomial is“x¹⁶+x¹⁵+x¹³+x⁴+1”, meaning a XOR operation on the 16th and 15th bits,then on the first result and 13rd bit, then on the second result and 4thbit, to generate the new bit.

On a receiver device side, a target register receives a first sequenceof n bits sent by the source register, uses the same feedback polynomialto determine the subsequent state of the target register, as expected,thus predicts the next bit to be transmitted and compares the nextreceived bit with the predicted bit.

The above method could also be used to compare bit sequences (forinstance 16 bit sequences) instead of performing a bit to bit comparisonto deal with a “sample by sample” transfer, as it is usual for audiosystems. Samples in such system are “signed integer” representation ofacoustical samples. Nevertheless, applying random bit sequence to suchsample is a valid way of filling them.

Such method for testing a signal transmission allows to evaluate if thesignal is correctly transmitted through the network on the basis of abit to bit comparison. It is commonly used for testing electronicallinks.

However, such bit to bit error measurement is not adequate for testingthe quality of the signal transmission in certain types of system ornetwork, for example for testing digital sounds transmitted through anautomotive audio architecture which typically includes several audiosubsystems and their interfaces such as interfaces between different ICs(Integrated Circuit) and also interfaces between ECUs (ElectronicControl Unit) in the vehicle like MOST (Media Oriented Systems Transportbus) or Ethernet AVB (Audio Video Bridging) from Head Units toAmplifiers. The subsystems and interfaces may create small variations inthe transmitted audio samples, due for instance to rounding errorsinduces by type conversion in software in the various network nodes orsmall deviations caused by digital sample rate conversion methods thatmight apply to a given audio channel. These variations and deviationsare random in their occurrence and importance, which means that theycould randomly appear (or not) in the system or network over time and ata random degree of importance. But other than random bit errors anywherein a sample, the nature of above mentioned tolerable error is to be arelatively small arithmetical difference of the real value of eachsample. Furthermore, as bit samples of audio signals sent by the sourceregister are altered through the system or network before arriving tothe target register, the BER test is likely to fail.

However, even if audio channels in an automotive digital audio systemmay degrade a transported audio signal corresponding to an audiomessage, said audio message could still be rated as fully audible andnot noticeably degraded, when it is played by a loudspeaker to alistener.

Being able to evaluate the quality of an audio transmission in a vehiclebecame crucial as audio messages highly impacts on the user automotiveexperience at various levels, from leisure to security.

Furthermore, obtaining information on the quality of audio signalstransmitted through an audio system or network, such as an audioarchitecture of a vehicle, is needed in different situations:

-   -   at design and design validation time, simple quality check of        audio distribution in automatable way (not dependent on proper        speaker setup) on test benches;    -   when the audio system is manufactured, in order to guarantee an        expected quality of the audio system,    -   when the audio system is used (for example, when the vehicle is        driven), for each emitted audio signal, to ensure that sensitive        audio messages, like audio functional safety relevant messages,        are correctly provided to the user(s) (for example, the vehicle        occupant(s)).

SUMMARY OF THE DISCLOSURE

The present disclosure concerns a method for testing the quality of asignal transmission in a communication system, comprising generating asignal comprising a succession of first bit sequences X_(n) with n=0, 1,2, . . . , wherein each first bit sequence X_(n) with n≥1 is determinedfrom the preceding first bit sequence X_(n−1) and using a deterministicalgorithm P; sending the signal from a transmitter device to a receiverdevice through the communication system; for each first bit sequenceX_(n) of the signal transmitted through the communication system,receiving, by the receiver device, a second bit sequence X_(n)′; and,for each second bit sequence X_(n)′ with n≥1, determining a first groupof candidates

corresponding to a plurality of possible first bit sequences X_(n,i)with i=0, 1, 2, . . . that could have been sent from the transmitterdevice and changed into the second bit sequence X_(n)′ according to anacceptable modification in the communication system, defined by atolerated and expected error; determining a second group of candidates

with j=0, 1, 2, . . . from candidates

determined from a preceding second bit sequence X_(n−1)′ and using thedeterministic algorithm P; intersecting the first group of candidates

and the second group of candidates

, by determining the candidates that are present in both the first groupof candidates

and the second group of candidates

, in order to determine a third group of candidates

; and checking said third group of candidates

in order determine the quality of the signal transmission.

In an aspect of the present disclosure, in the step of checking g), whenthe number of candidates of the third group is equal to zero, it isdetermined that the quality of signal transmission is insufficient.

Advantageously, for index n with n≥2, in step e), the second group ofcandidates

with j=0, 1, 2, . . . is determined from the candidates

of the third group determined for index n−1 and using the deterministicalgorithm P.

The signal may occupy all bit positions of a source register of thetransmitter device.

Alternatively, the signal may occupy all bit positions of a sourceregister of the transmitter device excluding a set of least significantbits of the source register. It allows to reduce the calculation effortbut also the test coverage.

In an aspect of the present disclosure, the signal is injected in a mainsignal to be transmitted from the transmitter device to the receiverdevice through the communication system, and occupies a part of the bitpositions of a source register of the transmitter device, the remainingbit positions of the source register being occupied by the main signal.Advantageously, each first bit sequence X_(n) replaces a set of theleast significant bits of the main signal in the source register.

Advantageously, the steps d) to g) are repeated as long as the thirdgroup of candidates includes at least one candidate.

Advantageously, if the third group includes at least one candidate whenall second bit sequences of the signal have been received, it isdetermined that the quality of the signal transmission is good.

According to an aspect of the present disclosure, the first group ofcandidates

determined according to a tolerance information that includes two limitvalues of tolerance, respectively minimal and maximal, and, for eachsecond bit sequence X_(n)′, the minimal tolerance value and the maximaltolerance value are calculated from the decimal value of the second bitsequence X_(n)′.

The minimal limit value of tolerance can be equal to the decimal valueof the second bit sequence X_(n)′ reduced by x % and the maximal limitvalue of tolerance can be equal to the decimal value of the second bitsequence X_(n)′ increased by x %, wherein x is comprised between 2 and20, preferably between 5 and 15.

Alternatively, the minimal limit value of tolerance can be equal to thedecimal value of the second bit sequence X_(n)′ reduced by a fixedamount τ and the maximal limit value of tolerance can be equal to thedecimal value of the second bit sequence X_(n)′ increased by said fixedamount τ, wherein τ is comprised between 2 and 20, preferably between 5and 15.

In an aspect of the present disclosure, the signal is an audio signal.

In an aspect of the present disclosure, in the step of checking g), whenthe third group has only one candidate, it is determined that thetransmitter and the receiver are in sync.

Advantageously, after the transmitter and the receiver are determined tobe in sync for index no, the method proceeds, for each of the nextindices n, with n>n₀, with comparing the received second bit sequenceX_(n)′ and a bit sequence generated from said one candidate and usingthe deterministic algorithm P in order to find a match.

When the transmitter and the receiver are in the “in sync” state, themethod may transit into a mode of error counting. It means that thenumber of consecutive errors are counted like in a classical bit errortester.

Advantageously, when no match is found several consecutive times for anumber of consecutive indices n, said number being superior to apredetermined value, it is determined that the transmitter and thereceiver are out of sync.

The test method as previously defined can be applied to test thetransmission of an audio signal in a vehicle architecture.

The test method can be applied during manufacturing of the vehicleand/or when the vehicle is used.

Another aspect of the present disclosure concerns a system for testingthe quality of a signal transmission in a communication system,comprising a generation unit configured to generate a signal comprisinga succession of first bit sequences X_(n) with n=0, 1, 2, . . . ,wherein each bit sequence X_(n) with n≥1 is determined from thepreceding first bit sequence X_(n−1) and using a deterministic algorithmP; a transmitter device for sending the signal through the communicationsystem; a receiver device for receiving the signal and configured, foreach first bit sequence X_(n) transmitted through the communicationsystem, to receive a second bit sequence X_(n)′; and a determining unitconfigured, for each of second bit sequences X_(n)′ with n≥1, todetermine a first group of candidates

corresponding to a plurality of possible first bit sequences X_(n,i)with i=0, 1, 2, . . . that could have been sent from the transmitterdevice and changed into the second test bit sequence X_(n)′ according toan acceptable modification in the communication system, defined by atolerated and expected error; determine a second group of candidates

with j=0, 1, 2, . . . from candidates

determined from a preceding second bit sequence X_(n−1)′ and using thedeterministic algorithm P; intersect the first group of candidates

and the second group of candidates

, by determining the candidates that are present in both the first groupof candidates

and the second group of candidates

, in order to determine a third group of candidates

; and check the third group of candidates

in order to determine the quality of the signal transmission.

Another aspect of the present disclosure concerns a receiver devicecomprising means for receiving a signal transmitted through acommunication system, said signal comprising a succession of first bitsequences X_(n) with n=0, 1, 2, . . . , wherein each first bit sequenceX_(n) with n≥1 is determined from the preceding first bit sequenceX_(n−1) and using a deterministic algorithm P, and means for determiningthe quality of the signal transmission by performing steps d) to g) ofthe method previously defined for each of the received sequences X_(n)with n≥1.

Another aspect of the present disclosure concerns a computer programcomprising instructions which, when the program is executed by acomputer, cause the computer to receive a signal transmitted through acommunication system, said signal comprising a succession of first bitsequences X_(n) with n=0, 1, 2, . . . , wherein each first bit sequenceX_(n) with n≥1 is determined from the preceding first bit sequenceX_(n−1) and using a deterministic algorithm P, and means for determiningthe quality of the signal transmission by performing steps d) to g) ofthe method previously defined for each of the received sequences X_(n)with n≥1.

Another aspect of the present disclosure concerns an audio testequipment integrating the system defined above, configured to test theaudio quality of the architecture of a vehicle.

Another aspect of the present disclosure concerns a vehicle integratingthe system defined above and/or the audio test equipment defined above.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, purposes and advantages of the present disclosure willbecome more explicit by means of reading the detailed statement of thenon-restrictive embodiments made with reference to the accompanyingdrawings.

FIG. 1 shows a schematic diagram of a communication system orarchitecture or network 100 according to an exemplar embodiment of thepresent disclosure.

FIG. 2 shows a flowchart representing a test method or process fortesting the quality of a signal transmission through the communicationsystem of FIG. 1, according to a first embodiment.

FIG. 3 shows an example of a bit register, more precisely a LFSR (LinearFeedback Shift Register).

FIG. 4 shows a schematic representation of the test process, accordingto the first embodiment.

FIG. 5 represents an example related to a second embodiment.

DETAILED DESCRIPTION OF THE DISCLOSURE

Before discussing example embodiments in more detail, it is noted thatsome example embodiments are described as processes or methods depictedas flowcharts. Although the flowcharts describe the operations assequential processes, some of the operations may be performed inparallel, concurrently or simultaneously and the order of operations maybe re-arranged. The processes may correspond to methods, functions,procedures, subroutines, subprograms, etc.

Specific structural and functional details disclosed herein are merelyrepresentative for purposes of describing example embodiments of thepresent disclosure. This present disclosure may, however, be embodied inmany alternate forms and should not be construed as limited to only theembodiments set forth herein.

Below, details of the present disclosure will be further provided incombination with the accompanying drawings.

FIG. 1 shows a system 200 comprising a transmitter device 1, acommunication system or architecture or network 100, and a receiverdevice 2, according to a first embodiment. For example, the system 200as shown in FIG. 1 is implemented in a vehicle to transmit audio digitalsignals. In this example case, the communication system 100 is anautomotive audio system or architecture.

The present disclosure is not limited to the transmission of audiodigital signals but may be applied to the transmission of any othertypes of digital signals (image, video, text, etc.).

In the system 200 implemented in a vehicle, the transmitter device 1 isfor example a sound processor and the receiver device 2 is for example aloudspeaker. The communication system 100 comprises one or more audiosubsystems (for example, interfaces between different integratedcircuits or electronic control units, network elements or nodes, etc.)and audio channels. The transmitter device 1 is configured to send anaudio signal to the receiver device 2, the signal being divided intosuccessive samples of L-bit length, for example in samples of 16-bitlength. The audio signal composed of the L-bit audio samples is thentransported through the communication system 100 and received by thereceiver device 2. The transmission in the communication system 100 islikely to cause small variations in the audio samples and thus mayimpact the quality of the signal transmission.

The transmitter device 1 includes a source bit register 10. The receiverdevice includes a target bit register 20. The source register 10 and thetarget register 20 are both of L-bit length.

The communication system 100 includes a test system for testing thequality of signal transmission from the transmitter device 1 to thereceiver device 2 through the communication system 100.

The test system comprises a generation unit 3 configured to generate asignal, noted S_(test). The signal S_(test) comprises a succession offirst bit sequences or samples X_(n) with n=0, 1, 2, . . . . Theoriginal bit sequence (or sample) X₀ is initially set. For example, itis a fixed value or a random value. X₀ is called a “seed” and must bedifferent a sequence of only “0”. Each bit sequence X_(n) with n≥1 isdetermined from the preceding bit sequence X_(n−1) and using adeterministic algorithm P. In other words, each bit sequence X_(n) withn≥1 can be expressed as follows: X_(n)=P (X_(n−1)).

In the first example embodiment, the deterministic algorithm P is a PRBS(Pseudo Random Binary Sequence) algorithm. The generation unit 3includes for example a LFSR (Linear Feedback Shift Register) comprisingthe source bit register 10 and a control unit 11. The control unit 11 isconfigured to control the generation of the first bit sequences X_(n)with n=0, 1, 2, . . . of the signal S_(test) by the source register 10,according to a PRBS algorithm.

Any other deterministic algorithm may be used instead of PRBS.

The test system also comprises a determining unit 4 to determine thequality of the signal transmission. The determining unit 4 is providedon the reception side. It is integrated in the receiver device 2.Alternatively, the determining unit 4 may be implemented externally withrespect to the receiver device 2 and connected to the receiver device 2.The operations and functions of the determining unit 4 will be describedin more detail in the description of the test process for testing thequality of a signal transmission from the transmitter device 1 to thereceiver device 2 through the communication system 100.

The generation unit 3 and the determining unit 4 may be functionsimplemented in a single processor or CPU (central processing unit).Alternatively, the generation unit 3 and the determining unit 4 areimplemented in two different processors or CPUs.

The use of a deterministic algorithm P, such as PRBS, allows to:

-   -   generate a succession of first bit sequences X_(n) with n=0, 1,        2, . . . to be transmitted from the source register 10 to the        target register 20, through the communication system (an audio        system in the example embodiment) to be tested, and    -   filter the received bit sequences, called hereinafter the        “second bit sequences”, so as to assess whether the quality of        transmission is inside a tolerance band or not.

The source register 10 and the target register 20 are of length L, Lbeing a number of bits. The value L corresponds preferably to the length(or number of bits) of signal samples, such as audio samples, to betransmitted. For example, L is equal to 16 bits. However, L may be equalto another value, preferably 2^(P) with p=2, 3, 4, 5 . . . .

The length of the bit sequences X_(n) of the signal S_(test) is m bits.Preferably, m L which means that, according to the embodiment, k=L orm<L, as described in the following description. In the first case (m=L),the signal S_(test) occupies all bit positions of the source register10. In the second case (m<L), the signal S_(test) occupies a part of thebit positions of the source register 10.

In order to evaluate the quality of a signal transmission through thecommunication system 100, a tolerance information such as a toleranceband is defined. This tolerance information indicates the maximal amountof modifications or alterations that a digital signal sent from thesource register 10 and transmitted through the communication system 100to the receiver device 2 can undergo, so that the received signal canstill be identified to the signal as originally sent when it is providedto a user (for example as an audio message).

A first embodiment of the test method or process will now be describedin more detail in reference to FIG. 2.

The test method comprises a step S0 of generating a signal S_(test)comprising a succession of first bit sequences X_(n) with n=0, 1, 2, . .. , wherein each first bit sequence X_(n) with n≥1 is determined fromthe preceding first bit sequence X_(n−1) and using a deterministicalgorithm P. In the present embodiment, the deterministic algorithm P isa pseudorandom binary sequence algorithm (PRBS). The bit sequences X_(n)are generated from a seed bit sequence S₀ that is chosen randomly. Then,for n≥1, each first bit sequence X_(n) can be expressed as follows:X_(n)=P(X_(n−1)).

In the first embodiment, the length m of each of the bit sequences X_(n)with n=0, 1, 2, . . . , is equal to the length L of the source register10. So, each first bit sequence X_(n) occupies all bit positions of thesource register 10.

In an illustrative example, given for the purpose of betterunderstanding the first embodiment, the length L is 16 bits. The sourceregister 10 is a 16-bit LFSR and the arrangement of bit positions thataffect the next state of the register, also called the “taps”, used forfeedback in the LFSR, can be expressed as a polynomial ofx¹⁶+x¹⁴+x¹³+x¹¹+1 (wherein “1” is equivalent to x⁰). The coefficients ofthe polynomial are “1” or “0”. In this feedback polynomial as shown onFIG. 3, the taps are at the 16th, 14th, 13th and 11th bit positions.

The first bit sequences X_(n) with n=0, 1, 2, . . . , are sent from thetransmitter device 1, more precisely from the source register 10, to thereceiver device 2 through the communication system 100, in a step S1.

On the reception side, the receiver device 2 receives second bitsequences X_(n)′, n=0, 1, 2, . . . , corresponding to the first bitsequences X_(n) that may have been altered in the communication system100 during transmission, in a step S2. In other words, for a first bitsequence X_(n) of the signal sent by the transmitter device 1 andtransmitted through the communication system 100, the receiver device 2receives a second bit sequence X_(n)′.

At a level “0” (for n=0) of the test process, the transmitter device 1generates and sends the first bit sequence X₀ (steps S0 and S1), or seedbit sequence X₀, and the receiver device 2 receives the second bitsequence X₀′ (step S2). Then, in a step S3, the determining unit 4determines a first group of candidates

corresponding to a plurality of possible first bit sequences X_(0,i)with i=0, 1, 2, . . . that could have been sent from the transmitterdevice and changed into the second bit sequence X₀′ according to anacceptable modification in the communication system 100. The range ofcandidates depends on a tolerance information, as will be explainedlater in the description.

Such “acceptable” modification of the sequence or sample may becharacterized by an arithmetic addition or subtraction of a toleratedand expected error, while a real error would be characterized by atotally unexpected value of a sample, for example because some highersignificant bits of the sample have flipped or one or more samples havebeen deleted. At a level “1” (for n=1) of the test process, thetransmitter device 1 generates and sends the first bit sequence X₁(steps S0 and S1), the receiver device 2 receives the second bitsequence X₁′ (step S2) and then steps S4 to S6, explained below, areperformed.

In step S4, the determining unit 4 determines a first group ofcandidates

corresponding to a plurality of possible first bit sequences X_(1,i)with i=0, 1, 2, . . . that could have been sent from the transmitterdevice and changed into the second bit sequence X₁′ according to anacceptable modification in the communication system 100. The range ofcandidates depends on a tolerance information that will be explainedlater in the description.

In addition, in step S5, the determining unit 4 determines a secondgroup of candidates

with i=0, 1, 2, . . . from the group of candidates

related to the second bit sequence X₀′ as received at level “0” andusing the deterministic algorithm P. More precisely, the deterministicalgorithm P is applied to each bit sequence X_(0,i) of the group ofcandidates

obtained at the preceding level “0” (for n=0) in order to determine thesecond group of candidates

of level “1” (n=1).

Then, in a subsequent step S6, the determining unit 4 determines a thirdgroup of candidates

by intersecting the first group of candidates

and the second group of candidates

determined in steps S4 and S5. In other words, the third group ofcandidates, or intersection group, includes the bit sequences that arepresent in both of the first group of candidates

and the second group of candidates

.

After step S6, the process goes to step S10 described later.

At each of the subsequent levels n with n≥2, for each second bitsequence X_(n)′ received by the receiver device 2, the following stepsS7 to S9 are performed.

In step S7, the determining unit 4 determines a first group ofcandidates

corresponding to a plurality of possible first bit sequences X_(n,i)with i=0, 1, 2, . . . that could have been sent from the transmitterdevice and changed into the second bit sequence X_(n)′ according to anacceptable modification in the communication system. The range ofcandidates depends on a tolerance information that will be explainedlater.

In step S8, the determining unit 4 determines a second group ofcandidates

with j=0, 1, 2, . . . from the third group of candidates

, or intersection group, related to the preceding second bit sequenceX_(n−1)′ (in other words, from the third group of candidates

obtained at the preceding level “n−1” of the process) and using thedeterministic algorithm P. The deterministic algorithm P is applied toeach bit sequence X_(n−1,k) of the group of candidates

obtained at the preceding level “n−1” (for n=0) in order to determinethe second group of candidates that is noted

of level “n”.

Then, in step S9, the determining unit 4 determines a third group ofcandidates

by obtaining an intersection between the first group of candidates

and the second group of candidates

. In other words, the determined candidates

are the candidates that are present in both of the first group ofcandidates

and the second group of candidates

.

In a following step S10 (also executed at level “1” for n=1 after stepS6), a test is executed to check the third group or intersection groupdetermined in step S9 (or S3). In step S10, it is determined whether thecurrent third group of candidates

includes at least one candidate or not. In other words, it is determinedwhether the current third group, as determined in step S9 (or S6), isempty or not.

If the third group of candidates, or intersection group, for the currentindex n is empty (“Yes” branch on FIG. 2), the test process goes to astep S12 wherein it is determined that the quality of the signaltransmission through the communication system 100 is insufficient. Instep S12, the determining unit 4 can send a notification indicating thatthe quality of transmission is insufficient, for example to an externalprocessor. A warning message indicating that the quality of the signaltransmission through the communication system 100 is insufficient may bedisplayed to the user and/or provided to an operator, such as anoperator of the manufacturer.

If the third group of candidates

, or intersection group, is not empty (“No” branch on FIG. 2), the testprocess goes to a next step S11, wherein it is checked whether a newsecond bit sequence (X_(n+1)′) has been received or not. The test canconsist in checking whether the current index n is equal to the totalnumber N or in checking the content of the target register. If a newsecond bit sequence X′_(n+1) has been received (“Yes” branch on FIG. 2),the process goes back to step S7, the index n being increased by one(“n=n+1”), and repeats the steps S7 to S10 for the following index n+1.

If no more second bit sequence has been received (or n=N), the processgoes to a step S13 wherein it is determined that the quality of thesignal transmission is sufficient (or good). A notification can be sentto an external processor indicating the information of good quality.

Thus, the loop comprising steps S7 to S10 is repeated until one of thetwo following situations occurs:

-   -   a. the current third group of candidates is empty (step S10,        “Yes” branch);    -   b. no new second bit sequence X′_(n) is received (or index n        reaches the maximal number N) with at least one candidate in the        third group (step S11, branch “No”).

In the first situation a) (the intersection group becomes empty on orbefore receiving the last second bit sequence X_(n)′ of the signal), thequality of signal transmission through the communication system 100 isdetermined as insufficient. In the second situation b), (a last secondbit sequence X_(n)′ of the signal is received while there is at leastone candidate in the intersection or third group), the quality of signaltransmission through the communication system 100 is determined assufficient or good.

The generation unit 3 is configured to perform step S0. The determiningunit is configured to perform steps S3 to S13.

FIG. 4 shows a schematic representation of the process described aboveat levels n=0, n=1 and n=2.

The process is performed on a total number N of first bit sequencesX_(n), forming the signal S_(test). The size or length of the signalS_(test) is preferably chosen in a range of usual sizes of a signaltransmitted from the transmitter device 1 to the receiver device 2through the communication system 100. The size of the signal S_(test)can be equal to the size of a reference signal. For example, the size ofthe signal S_(test) is an average value of a plurality of signalsusually transmitted from the transmitter device 1 to the receiver device2. In case of an audio communication system or architecture 100 in avehicle, the transmitter device 1 may be configured to transmitpredefined audio messages, such as security messages or userinstructions, of known time durations. The size of the signal S_(test)can be set to represent an average value of the known time durations ofthe predefined audio messages (security, user instructions, etc.). Thetotal number N (maximal value of index n) is calculated from the size ofthe signal S_(test). For example, the audio message is a spoken phraselike “Please take control of the vehicle and grab the steering wheelagain!”. Such an audio message may have 5 second duration.

The tolerance information indicates a maximal amount of modifications oralterations that a digital signal sent from the source register 1 andtransmitted through the communication system 100 to the receiver device2 can undergo, so that the received signal can still be identified tothe signal as originally sent. For example, in case of an audio signalcarrying an audio message and transmitted through a communicationsystem, a user listening the audio message played by a loudspeakershould be able to identify the original audio message as sent. Thetolerance information can comprise a minimal tolerance value and amaximal tolerance value that define a tolerance band. For each secondbit sequence X_(n)′ received by the receiver device 2, the minimaltolerance value and the maximal tolerance value are calculated from thedecimal value of the second bit sequence X_(n)′. For example, theminimal limit value of tolerance X_(n,min)′ can be equal to the decimalvalue of the second bit sequence X_(n)′ reduced by x % and the maximallimit value of tolerance X_(n,max)′ can be equal to the decimal value ofthe second bit sequence X_(n)′ increased by x %, which can be expressedas follows:X _(n,min) ′=X _(n) −x%·X _(n)′X _(n,max) ′=X _(n) −x%·X _(n)′

The value x of percentage can be comprised between 2 and 20, preferablybetween 5 and 15. For example, x is equal to 10 and therefore:X _(n,min)′=90%·X _(n)′X _(n,min)′=110%·X _(n)′

Alternatively, the minimal limit value of tolerance X_(n,min)′ is equalto the decimal value of the second bit sequence X_(n)′ reduced by afixed amount τ and the maximal limit value of tolerance X_(n,max)′ isequal to the decimal value of the second bit sequence X_(n)′ increasedby said fixed amount τ. In other words:X _(n,min) ′=X _(n)′−τX _(n,max) ′=X _(n)′+τ

The value of the fixed amount τ can be comprised between 2 and 20,preferably between 5 and 15. For example, τ is equal to 10 andX _(n,min) ′=X _(n)′−10X _(n,min) ′=X _(n)′+10

In the first embodiment, the signal S_(test) occupies all bit positionsof the source register.

In a variant of the first embodiment, the signal S_(test) occupies allbit positions of the source register excluding a set of leastsignificant bits of the source register. In other words, a set of leastsignificant bits (LSB) are excluded from the test. Thanks to that, thecalculation effort of the test is reduced. The calculation time durationis reduced, which allows to reduce test time duration and/or use asmaller processor (CPU) to execute the test.

In case the deterministic algorithm is a bijection (which is the casefor a feedback polynomial), it is possible, starting from a third groupof candidates at any stage, to determine all the possible successive bitsequences that have been sent to generate the third group of candidatesand the deviations they went through.

The test method is realized in a distributed computing environment. Thepresent disclosure concerns the distributed system including thetransmitter device 1 and the receiver device 2 and each entity of thedistributed system, i.e. the transmitter device 1 and the receiverdevice 2.

Furthermore, the test method is advantageously implemented by a firstcomputer, on the transmitter side, and by a second computer, on thereceiver side. Therefore, the present disclosure also concerns:

-   -   a computer program comprising instructions which, when the        program is executed by the first computer, cause the first        computer to generate a signal by performing step S0 and to        transmit the signal to the second computer;    -   a computer program comprising instructions which, when the        program is executed by the second computer, cause the second        computer to receive the signal and to determine whether the        quality of the transmission by performing steps S3 to S13.

A second embodiment is based on the first embodiment and differs fromthe first embodiment only by the features described hereinafter.

In the second embodiment, the signal S_(test) is inserted in a mainsignal S_(m). In case of an audio communication system or architectureof a vehicle, the main signal can be an audio signal carrying an audiomessage, such as a security message or a user instruction, to be playedto the user.

The signal S_(test) is injected in the main signal S_(m) to betransmitted from the transmitter device 1 to the receiver device 2through the communication system 100.

The signal S_(test) comprises a succession of first bit sequences X_(n)with n=0, 1, 2, . . . , as previously described. The length m of each ofthe first bit sequences X_(n) is strictly inferior to the length L ofthe source register and/or the samples of the main signal S_(m). Thesignal S_(test) occupies a part of the bit positions of the sourceregister 10, the remaining bit positions of the source register 10 beingoccupied by the main signal S_(m). More precisely, m bit positions ofthe source register 10 are occupied by a first bit sequence X_(n) of thesignal S_(test) and the L−m remaining bit positions are occupied by bitsof a sample of the main signal S_(m).

Advantageously, each first bit sequence X_(n) replaces a set of q leastsignificant bits of the main signal S_(m) in the source register 10. Inorder words, in the source register 10, or in each sample of length L ofthe main signal S_(m), a set of least significant bits of the mainsignal S_(m) are deleted and replaced by a first bit sequence X_(n) ofthe signal S_(test). For instance, the first bit sequence X_(n) replacesthe five least significant bits of the source register 10.

The deterministic algorithm p is applied only to bits of the signalS_(test) in the source register 10.

In the second embodiment, the injection of the signal in the main signalis introduces test bit sequences in the main signal. The modification ofthe main signal is adapted to be assimilated to a white noise that canhardly be perceived by a user (a listener in case of audio signals).This is achieved by all or part of the following features:

-   -   The deterministic algorithm P is a PRBS algorithm. Such        algorithm generates random sequences of bits, which, by their        random nature, can be assimilated to white noise by users (e.g.        listeners).    -   The bits of the signal S_(test) occupy only a small fraction of        the source and target registers, preferably a part A including        the LSB (least significant bits), for instance the five LSB, so        that users (e.g. listeners) hardly perceived the part A and        could mistake it for small noise floor.    -   The main signal (e.g. the useful audio message) occupies the        other part of the source and target registers. So, for each bit        sequence sent from the source register 10, some of the LSB are        used for the test process and the other bits are for the main        signal itself.

A third embodiment will now be described with reference to FIG. 5. It isbased on either the first embodiment or the second embodiment and onlydiffers from these embodiments by the features described hereinafter.The third embodiment allows to determine if the transmitter and thereceiver are in sync or out of sync (or in a “sync loss” state).

According to the third embodiment, steps S0 to S9 are performed, as willbe explained now. The checking step S10 is also executed and, in stepS10, it is checked whether the third group has only one candidate ornot. If the third group includes only one candidate, it is determinedthat the transmitter and the receiver are in sync. It means that thereceiver receives the bit sequence or sample as sent by the transmitter,without modification. Consequently, the quality of transmission isconsidered as very good.

Then, after the transmitter 1 and the receiver 2 are determined to be ina “in sync” state, for example at index no, the method proceeds, foreach of the next indices n with n>n₀, with comparing the received secondbit sequence or sample X_(n)′ and a bit sequence or sample generatedfrom said one candidate and using the deterministic algorithm P, inorder to find a match. When no match is found X times for X consecutiveindices n, X being superior to a predetermined limit value (for example1, 2 or more), it is determined that the transmitter 1 and the receiver2 are out of sync or in a state “sync loss”. In that case, the methodreturns to the beginning (step S0) and starts again. The predeterminedlimit value may be comprised between 1 and 100, preferably between 1 and50, more preferably between 5 and 20, for example the limit value isequal to 10.

The third embodiment may be executed in combination with the first orthe second embodiment or alone, independently of the first or secondembodiment.

FIG. 5 represents an exemplary diagram that allows to illustrate thethird embodiment. X₀, X₁ and X₂ on the left of the diagram are threesamples or sequences, generated by the transmitter 1. For example, eachsequence includes 16 bits. X₁ is built by applying the deterministicalgorithm P to X₀ as a start condition or seed. The transmitter 1 thencontinues by generating X₂, X₃, X₄ in the same manner.

The transmitter 1 sends X₀ to the receiver 2, through the communicationsystem 100. The sequence X₀ is assumed to suffer a tolerable errorduring its transmission through the communication system 100. Thereceiver 2 receive the sample X′₀. When the transmitter 1 and thereceiver 2 are out of sync, the receiver 2 has no history data. It onlyhas the definition of the deterministic algorithm P and the assumptionof a tolerable error due to transmission in the communication system100. So, when the sequence X′₀ is received, the receiver 2 can onlyassume to have gotten either the 16 valid bits of the sequence X₀ assent, or an arithmetic deviation to that 16 Bit sequence X₀, that isconsidered as a tolerable error. This makes up a field of potential sentsequences. For example (only for a purpose of illustrating the thirdembodiment), the potential sent sequences are five and noted X_(0a),X_(0b), X_(0c), X_(0d) and X_(0e) on FIG. 5. Let's assume that thedecimal value of X₀ is “50” and a tolerance band is “2”, then thedecimal values of X_(0a), X_(0b), X_(0c), X_(0d) and X_(0e) are 48, 49,50, 51 and 52. For example, the transmitter 1 could have sent 49 and itcould have been received as 48. The transmitter could as well have sent50, and it could have been received as 49. The receiver 2 cannot know.

As the receiver 2 has no more information at this moment, it generates anext candidate Y_(0a), Y_(0b), Y_(0c), Y_(0d) and Y_(0e) for each of thepotential sent sequences or samples X_(0a), X_(0b), X_(0c), X_(0d) andX_(0e) by applying the deterministic algorithm P (step S5).

Then, the next sequence X₁ (generated from X₀ by applying the algorithmP) is sent by the transmitter 1. Again, the receiver 2 assumes atolerable error of transmission and will build up the potential sentsequences potential sent sequences or samples X_(1a), X_(1b), X_(1c),X_(1d) and X_(1e). But now, the receiver 2 is in a “synchronizing”process, as it has already historical data of previous sample orsequence. The receiver 2 compares X_(1a), X_(1b), X_(1c), X_(1d) andX_(1e) with Y_(0a), Y_(0b), Y_(0c), Y_(0d) and Y_(0e) (step S6). Itidentifies all matches (there can be more than one match) and savesthem. In the present example illustrated on FIG. 5, there are twomatches: M_(1a), M_(1b).

Then, again, the algorithm P is applied to generate two candidatesY_(2a) and Y_(2b) for the next expected sample or sequence (step S8).

The transmitter 1 then sends the next sample or sequence X₂ and, aftertransmission through the communication system, the receiver 2 receivesthe sample X′₂. When this next sample or sequence X′₂ is received, allthe potential sent variations X_(2a), X_(2b), X_(2c), X_(2a) and X_(2e)of the sent sample X₂ are generated by the receiver 2 (step S7). Then,the receiver 2 compares the two candidates Y_(2a) and Y_(2b) and X_(2a),X_(2b), X_(2c), X_(2d) and X_(2e).

In the present example, it is determined that now only one match M₂ isfound (in the checking step S10). It means that the alignment of thePRBS sequence between transmitter and receiver is perfect. Consequently,it is determined that the receiver 2 and the transmitter 1 are in sync.

From this stage of the process, there is no need to further investigatemore candidates. It means that the receiver 2 no longer generatesseveral candidates when it receives a new sample or sequence.

The receiver may alternatively simply generate a next one candidate fromthe single previous one using the deterministic algorithm P and compareit to the next received sample.

In case the comparison provides a match, it is determined that thereceiver 2 and the transmitter 1 remain a state “in sync”.

In case the comparison no longer provides a match, which means that thereceived sample is different from the one candidate generated from theprevious one using the algorithm P, it is determined that the receivedsample includes an error, called a “sample error”. An error counter isthen started to count the number of consecutive errors or “sampleerrors”. Anyhow, the receiver 2 uses the one candidate to generate a newexpected sample for next sample to be received. When the next sample isreceived, both samples (expected sample that has been generated from theone candidate and the received sample) are compared. If a match isfound, the counter is stopped and the receiver 2 and the transmitter 1are determined to be in sync again. If no match is found, the counter isincreased by one.

Thus, as long as the transmitter 1 and the receiver 2 are in the “insync” state, the receiver may transit into a mode of error counting. Itmeans that the receiver may count the number of consecutive errors likea classical bit error tester.

A limit value of consecutive sample errors may be predefined. If theamount of consecutive errors in the counter reaches this limit value, itmay be determined or detected that the transmitter 1 and the receiver 2are out of sync or in a state of “sync loss”. This limit value may beequal to only one or more than one. As previously indicated, thepredetermined limit value may be comprised between 1 and 100, preferablybetween 1 and 50, more preferably between 5 and 20, for example thelimit value is equal to 10.

Then, the receiver 2 returns to the first step of the process, at thebeginning of the diagram of FIG. 5 (or step S0 of FIG. 2). The processis executed from the beginning again in order to search for a “in sync”state of the transmitter and the receiver.

Alternatively, after finding no match of the single candidate, thereceiver 2 could right away determine that the transmitter and thereceiver are out of sync and return to the first step of the process.

As described above, the third embodiment executes steps S1 to S10 shownin FIG. 2. In the checking step S10, it is checked whether the thirdgroup of candidates includes only one candidate. If so, the method stopsdetermining a group of several candidates when a new sample or secondbit sequence is received and proceeds with comparing the received secondbit sequence X_(n)′ and a bit sequence generated from the one candidateand using the deterministic algorithm P, in order to find a match. Aslong as a match is found, the transmitter and the receiver are detectedto be in sync. When no match is found several consecutive times, for anumber of consecutive indices n superior to a predetermined value, it isdetermined that the transmitter and the receiver are out of sync.However, it may be determined that the transmitter and the receiver areout of sync as soon as no match is found once.

The receiver 2 includes a target bit register 20 and a determining unit4 configured to execute the third embodiment as described above.

On the receiver side, the third embodiment may be implemented by acomputer program comprising instructions which, when the program isexecuted by a computer, cause the computer to receive a signaltransmitted through the communication system 100, said signal comprisinga succession of first bit sequences X_(n) with n=0, 1, 2, . . . ,wherein each first bit sequence X_(n) with n≥1 is determined from thepreceding first bit sequence X_(n−1) and using a deterministic algorithmP, and means for determining whether the transmitter 1 and the received2 are in sync, as described above.

The present disclosure is suitable to be integrated in a test equipmentand could be applied to check the overall transmission quality of acommunication system or network during manufacturing.

The first embodiment is suitable to be applied to check the quality of atransmission system during or at the end of manufacturing.

The second embodiment is suitable to be applied to check the quality ofa communication system in use (e.g. when a vehicle including the audioarchitecture is driven).

The test method is able to classify the quality or “clearness” of agiven audio channel for the reasons explained below.

The test process can show the deviations that samples had undergone, incase there is only one candidate left in the third group of candidatesand if the deterministic P is a bijection. The test process can alsoprovide a probabilistic distribution of these deviations, in case thereare several candidates left in the third group of candidates or if P isnot a bijection).

Furthermore, the test method can provide the count of errors which hasbeen beyond the accepted tolerance (the number of times there is no morecandidates in a third group of candidates).

The test method can also indicate events of sync loss (loss ofsynchronization), for instance due to dropped audio buffers, when thethird group of candidates reaches no candidate left.

In case the communication system comprises a mixing device between thesource register and the target register, which mixes and/or combines bitsequences coming from different sources including the source register,such mixing device should not change the part A occupied by the testbits used for testing the quality. In other words, the mixing deviceshould act as a “bit mask” mixer for part A.

The way of testing of the present disclosure is in particular suited tocatch some problems that are coming from the nature of digital signalhandling, in particular:

-   -   rounding problem from variable type conversion (floating point        to fixed point along the processing and transmission chain);    -   unawareness of implicit sample rate conversion (e.g. in the SW        stack of Linux ALSA architecture, where without obvious reason a        sample rate conversion might have happened, for instance from a        48 kHz source to 44.1 kHz of a sound card output in one ECU and        a back conversion to 48 kHz in the other ECU);    -   problem of lost sample groups (buffers), for instance when        somewhere in the processing and transmitting chain, due to lack        of processing power, underrun situations (buffer fed at a lower        speed than it is being read) occurred.

The test method uses the fact that the first bit sequences X_(n) withn=0, 1, 2, . . . are pseudorandom bit sequences that seem random but caneach be determined from a preceding first bit sequence. These first bitsequences can be assimilated to white noise by users (e.g. listeners foraudio signals). A PRBS signal replaces the least significant bits (LSB)of the main signal, creating some little, not disturbing noise floor,and the indicated method is used on the PRBS to check whether the LSB,and so the main signal, are inside a defined a tolerance band or not.

The present disclosure allows to estimate the clearness and quality of adigital transport network as well as to assess the quality oftransmitted signals distributed on such network.

The quality of the audio channel (real deviation, number of errors etc.)can also be evaluated by the present disclosure.

The present disclosure can also be used to detect and prove the playbackof an audio stream even when such audio stream is mixed with other audiosignals.

The present disclosure also concerns:

-   -   an audio test equipment integrating the test system previously        described, configured to test the audio quality of the        architecture of a vehicle, and    -   a vehicle integrating the described system or the above audio        test equipment.

The invention claimed is:
 1. A method for testing a quality of a signaltransmission in a communication system, the method comprising: a)generating a signal comprising an initial bit sequence X₀ and asuccession of bit sequences X_(n) wherein n=1, 2, . . . , wherein eachbit sequence X_(n) with n≥1 is determined by applying a deterministicalgorithm P to a preceding bit sequence X_(n−1) of the signal; b)sending the signal from a transmitter device to a receiver devicethrough the communication system; c) receiving, by the receiver device,a succession of received bit sequences X_(n)′ wherein n=0, 1, 2, . . . ,and wherein each received bit sequence X_(n)′ corresponds to each bitsequence X_(n) of the signal transmitted through the communicationsystem; d) determining a first group of candidates {X_(n,i)}_(i∈N) foreach received bit sequence X_(n)′ with n≥1, wherein each first group ofcandidates corresponds to a plurality of possible sent bit sequencesX_(n,i) with i=0, 1, 2, . . . modified by a signal modification in thecommunication system defined by a tolerated and expected error; e)determining a second group of candidates {Y_(n,j)}_(j∈N) for eachreceived bit sequence X_(n)′ with n≥1 and j=0, 1, 2, by applying thedeterministic algorithm P to the first group off candidates{X_(n−1,k)}_(k∈N) determined from the first group of candidates for apreceding received bit sequence X_(n−1)′; f) determining a third groupof candidates {X_(n,k)}_(k∈N) by intersecting the first group ofcandidates {X_(n,i)}_(i∈N) and the second group of candidates{Y_(n,j)}_(j∈N) and including candidates that are present in both thefirst group of candidates {X_(n,i)}_(i∈N) and the second group ofcandidates {Y_(n,j)}_(j∈N) in the third group of candidates{X_(n,k)}_(k∈N); and g) determining the quality of the signaltransmission based on a number of candidates in the third group ofcandidates {X_(n,k)}_(k∈N).
 2. The method according to claim 1, whereindetermining the quality of the signal transmission comprises determiningthat the quality of signal transmission is insufficient when the numberof candidates of the third group is equal to zero.
 3. The methodaccording to claim 1, wherein, for n≥2, the second group of candidates{Y_(n,j)}_(j∈N) with j=0, 1, 2, . . . is determined from the candidates{X_(n−1,k)}_(k∈N) of the third group determined for index n−1 and usingthe deterministic algorithm P.
 4. The method according to claim 1,wherein the signal occupies all bit positions of a source register ofthe transmitter device.
 5. The method according to claim 1, wherein thesignal occupies all bit positions of a source register excluding a setof least significant bits of the source register.
 6. The methodaccording to claim 1, wherein the signal is injected in a main signal tobe transmitted from the transmitter device to the receiver devicethrough the communication system, the signal occupies a part of bitpositions of a source register of the transmitter device, and remainingbit positions of the source register are occupied by the main signal. 7.The method according to claim 6, wherein each bit sequence X_(n)replaces a set of the least significant bits of the main signal in thesource register.
 8. The method according to claim 1, wherein determiningthe first, second and third groups of candidates and determining thequality of the transmission are repeated as long as the third group ofcandidates includes at least one candidate.
 9. The method according toclaim 8, wherein, if the third group of candidates includes at least onecandidate when all received bit sequences of the signal are received, itis determined that the quality of the signal transmission is good. 10.The method according to claim 1, wherein the first group of candidates{X_(n,i)}_(i∈N) is determined according to tolerance information thatincludes a minimal tolerance value and a maximal tolerance value and,for each received bit sequence X_(n)′, the minimal tolerance value andthe maximal tolerance value are calculated from a decimal value of thereceived bit sequence X_(n)′.
 11. The method according to claim 1,wherein determining the quality of the signal transmission comprisesdetermining that the transmitter device and the receiver device are insync when the third group of candidates has only one candidate.
 12. Themethod according to claim 11, wherein, after the transmitter device andthe receiver device are determined to be in sync for an index n=n₀, themethod proceeds, for each of a plurality of next indices n, with n>n₀,with comparing the received bit sequence X_(n)′ and a bit sequencegenerated from said one candidate and using the deterministic algorithmP in order to find a match.
 13. The method according to claim 12,wherein, when no match is found for a number of consecutive indices nexceeding a predetermined value, it is determined that the transmitterdevice and the receiver device are out of sync.
 14. The method accordingto claim 1, wherein the generated signal is an audio signal in a vehiclearchitecture.
 15. The method according to claim 14, wherein the methodis applied during manufacturing of the vehicle or when the vehicle isused.
 16. A system for testing a communication signal transmissionquality, the system comprising: a generation unit configured to generatea signal comprising an initial bit sequence X₀ and a succession of bitsequences X_(n) with n=1, 2, . . . , wherein each bit sequence X_(n)with n≥1 is determined by applying a deterministic algorithm P to apreceding bit sequence X_(n−1) of the signal; a transmitter device forsending the signal; a receiver device for receiving the signal as areceived bit sequence X_(n)′ for each bit sequence X_(n) transmitted bythe transmitter device, wherein n=0, 1, 2, . . . ; and a determiningunit including at least one processor configured to determine, for eachreceived bit sequence X_(n)′ with n≥1, a first group of candidates{X_(n,i)}_(i∈N) wherein each first group of candidates corresponds to aplurality of possible sent bit sequences X_(n,i) with i=0, 1, 2, . . .modified by a signal modification in the communication system defined bya tolerated and expected error; determine, for each received bitsequence X_(n)′ with n≥1, a second group of candidates {Y_(n,j)}_(j∈N)with j=0, 1, 2, . . . by applying the deterministic algorithm P to thefirst group off candidates {X_(n−1,k)}_(k∈N) from the first group ofcandidates fora preceding received bit sequence X_(n−1)′; determine athird group of candidates {X_(n,k)}_(k∈N) by intersecting the firstgroup of candidates {X_(n,i)}_(i∈N) and the second group of candidates{Y_(n,j)}_(j∈N)′ and including candidates that are present in both thefirst group of candidates {X_(n,i)}_(i∈N) and the second group ofcandidates {Y_(n,j)}_(j∈N), in the third group of candidates{X_(n,k)}_(k∈N); and determine the quality of the signal transmissionbased on a number of candidates in the third group of candidates{X_(n,k)}_(k∈N).
 17. The system of claim 16, wherein the signal is anaudio signal and the system is configured to test the audio quality ofan architecture of a vehicle.
 18. A non-transitory storage mediumincluding instructions that, when executed by at least one processor,cause the at least one processor to determine a transmission quality ofa received signal by determining, for each received bit sequence X_(n)′of the received signal with n≥1, a first group of candidates{X_(n,i)}_(i∈N) wherein each first group of candidates corresponds to aplurality of possible sent bit sequences X_(n,i) with i=0, 1, 2, . . .modified by a signal modification defined by a tolerated and expectederror; determining, for each received bit sequence X_(n)′ of thereceived signal with n≥1, a second group of candidates {Y_(n,j)}_(j∈N)with j=0, 1, 2, . . . by applying a deterministic algorithm P to thefirst group of candidates {X_(n−1,k)}_(k∈N) from the first group ofcandidates for a preceding received bit sequence X_(n−1)′; determining athird group of candidates {X_(n,k)}_(k∈N) by intersecting the firstgroup of candidates {X_(n,i)}_(i∈N) and the second group of candidates{Y_(n,j)}_(j∈N) and including candidates that are present in both thefirst group of candidates {X_(n,i)}_(i∈N) and the second group ofcandidates {Y_(n,j)}_(j∈N), in the third group of candidates{X_(n,k)}_(k∈N); and determining the quality of the signal transmissionbased on a number of candidates in the third group of candidates{X_(n,k)}_(k∈N.)